Railway road beds must be capable of supporting extremely heavy rolling stock. Road beds have traditionally included closely spaced railroad ties for supporting the railroad rails. The ties in turn are supported by ballast comprising essentially debris-free rocks through which rain water can drain quickly.
Maintenance of the ballast in a railway road bed is a primary concern in extending the usefulness of the railway road bed. The ballast must be periodically replenished to ensure that the ties and rails are supported by an adequate amount of ballast. Maintenance of a railway road bed by cleaning or tamping the track bed ballast also often requires addition of ballast to the bed.
Adding ballast to a railway road bed by conventional means is time-consuming, labor intensive and dangerous. The additional ballast is transported to the stretch of track it will be deposited on by railroad ballast hopper cars. The cars have lowermost discharge doors that can be selectively opened to allow ballast to flow out of the car under the influence of gravity.
As the ballast hopper cars move along the rails at two to three miles per hour, a crew member walks beside the ballast hopper cars opening and closing the discharge doors to deposit ballast. A long metal lever is placed by the crew member in a tube attached to the discharge door to be opened or closed. The crew member, while walking alongside the moving hopper car, pushes the lever up or down to pivot the discharge door open or closed. The discharge doors are generally oriented directly above a rail, and include a chute or chutes that can be pivoted to either side of the rail for depositing ballast to the field side or the gauge side of the rail.
Frequently, when a crew member moves the lever back to its original position to close the discharge door, pieces of ballast become wedged in the opening between the hopper discharge gate and the discharge door. The crew member must push the lever quickly up and down, moving the discharge door just enough to free the ballast and close the discharge door before any more ballast becomes wedged. As the crew member works to unblock the discharge door, excess ballast may be discharged, resulting in the waste of some ballast. Moreover, pushing the lever up and down is physically demanding, and distracts the crew member from attention to his personal safety as he walks alongside the moving train. Manual operation of hopper discharge doors is particularly dangerous when a discharge door must be quickly closed prior to the ballast hopper car transiting across a bridge, switch track, or other obstacle.
It will also be appreciated that the wedging of ballast between the discharge gate and the discharge door prevents full closing of the ballast hopper discharge door and is an obstacle to the automatic operation of the discharge doors. In that regard, a motor trying to completely close a discharge door that is blocked from closing by wedged ballast would continue to run and draw power while seeking the closed position, leading to failure of the motor.
A self-clearing discharge door that rarely becomes blocked by ballast would provide a decided advantage to the railroad maintenance industry in terms of manpower, ballast wastage, and safety. Moreover, a discharge door capable of self-clearing blocking ballast could be easily adapted for the automatic, motor-assisted movement of the discharge door.